First of all you have to remember that every time you will install a program, it will logically want to install on the C drive; so don't make it too small, you make get stuck on space.
Secondly, you could make a 1.5 Gig for you swap file. Ideally the swapfile shoule be 1.5 times the amount of RAM, but make it a bit bigger in case you install some more RAM.
From what I see you have a 40 Gig hard disk, why don't you buy another one, put the swapfile partition on it, as well as splitting it in 2, and leave the C drive as a unit.
You will have a big advantage of putting your swapfile on a separate hard drive and if you leave you operation system alone on its drive; if you have to reformat, you won;t have to touch the other drive and/or partitions.
Note: A swapfile by itself in its' own partition will barely fragment which helps the operating system run more smoothly.